In my pending application Ser. No. 798,983 now U.S. Pat. No. 4,677,772, filed Nov. 18, 1985, there is shown an excavator wherein a generally arcuate arm is pivotally supported at one end to a mobile carriage which has at its other end an excavator and structure for supporting it at said end. While the structure shown there is designed to increase the range of use and to minimize failure of the supporting beam, it cannot be used efficiently in tunnel operations due to lack of head room. While the Gradall Company builds an excavator wherein the excavator is supported by a boom which can be moved rectilinearly in a generally horizontal plane and so is adapted to be used in tunnel excavation, the backhoe is connected directly to the distal end of the boom and, hence, the structure lacks the range provided by the structure shown in the aforesaid pending application. It is the purpose of this invention to provide an excavator which will embody the advantages of construction of the excavator shown in the aforesaid pending application and the structure of the Gradall machine in such a way as to be uniquely adapted to tunnel excavation and, at the same time, to provide a much larger range of operation than can be achieved with the use of the Gradall excavator.